THE CHEMISTRY OF PHOTOSYNTHESIS 279 



d. The Condensation of Formaldehyde with Weak Alkalies and 

 Under the Influence of Light. 



Little consideration has been given to the question whether the con- 

 densation of formaldehyde actually takes place under conditions such as 

 may exist in the chloroplast, at least as far as the hydrogen ion concentra- 

 tion of the chloroplast is concerned. The writer has made a series of 

 tests to determine whether formose is formed from formaldehyde in 

 zveak alkaline or in' neutral solution and at ordinary temperatures and, 

 whether the reaction is influenced by sunlight. Pure 3 per cent solutions 

 of formaldehyde (free from methyl alcohol and formic acid) were used, 

 with the salts in tenth normal concentration, in glass flasks. These were 

 exposed directly to the sunlight in Arizona for five months, and the 

 amount of sugar formed determined every month. Not a trace of sugar 

 was formed by CaCOg, 3MgC03.Mg(OH),.3HX), K2CO3, KHCO3, 

 colloidal Fe(OH)3, in the dark or the sunlight. Potassium nitrate solu- 

 tions which become slightly alkaline when exposed to sunlight with the 

 formation of nitrite and traces of ammonia, produced very small quanti- 

 ties of sugar from formaldehyde in the light. Zinc carbonate also pro- 

 duced traces of sugar in the light. All of the solutions on evaporation 

 at reduced pressure left a residue of polymerized formaldehyde (para- 

 formaldehyde), but this is not a condensation product and disappears 

 on repeated addition of water and evaporation at reduced pressure. Only 

 such products which on evaporation at reduced pressure gave no test for 

 formaldehyde in the water which had been distilled from them and which 

 reduced Fehling solution were considered as condensation products. In 

 almost every case some formic acid had been formed. With the stronger 

 bases, lead hydroxide and calcium hydroxide, light increases the yield of 

 the formose obtained. The writer has also endeavored to obtain con- 

 densation of formaldehyde with weak optically active bases, such as brucine 

 and quinine, but the yields of sugar were always very small and never 

 showed any optical rotation. 



The condensation product obtained from formaldehyde is unquestion- 

 ably a mixture of a great many different substances, probably more than 

 Nef considered as being present. This becomes evident from the fact 

 that the reducing power of the formose mixture as determined with a 

 cuproalkaline solution is usually considerably lower than the amount cal- 

 culated from the weight of condensation product taken as sugar. With 

 stronger alkalies there are in all probability also some saccharinic acids 

 formed. 



Although the fact was not considered in the original Baeyer theory, 

 it is possible that light is necessary, or at least plays a part in the con- 

 densation of formaldehyde. That the condensation is affected by light 

 has been observed by various workers. Inghilleri ** reported that by ex- 

 posing sealed tubes containing formaldehyde to sunlight he obtained 



"Inghilleri, Zeit. physiol. Chem., 71, 105 (1911), 73, 144 (1912). 



